December in Clackamas is the windiest and the coldest month of the year. In December, the weather in Clackamas is typically cold. Average daily high temperature in December is about 6 degrees above zero. On average, Clackamas has 18 rainy, 6 sunny, 5 partly cloudy, and 2 cloudy days in December. The rains are usually heavy. December as well as January, February, March, and April is considered the most uncomfortable time to visit Clackamas.